Could be a low fill.

A common problem is the unit not filling with enough water.
Most units fill to just under the heating element.
This can be checked by adding a couple quarts of water after each fill during a cycle. If it now washes OK then check the fill valve.
Just be careful to not overfill it.
Often if the fill is low you will also hear a growling sound because the pump will cavitate (suck in air).
The most common cause is a dirty screen filter on the input side of the fill valve. Remove the valve from the unit and clean/check the filter.
Do not permanently remove it from the valve as it is there to keep crud out of the valve which could hold it open and cause a flood.

If it still does not fill correctly I would replace the fill valve.

PS: Be sure to shut off the power and the water supply to the unit. Have paper towels etc. handy to wipe up any spilled water. Get a small pan/bowl etc. that will fit under the valve then loosen the input water line let it drip into the container emptying it as necessary. This will minimize the amount of water spilled.

Also could be dirty filters or something impeding the pump.
Open the pump up and check the filters and that the impeller and chopper are clear.
Following is a manual which should help.
http://appliancejunk.com/forums/index.php?action=downloads;sa=view;down=231

Check the distribution assembly.
Click on the picture of Item 3 in Section 7 of the parts and a new page will open with more views and info.